Patent EA-000901-B1 (EA)
Title: A process for inhibiting scale precipitation in oil extraction and formulation therefor
Inventor: COLLINS IAN RALPH
IPC: C09K8/54
Filed: 1997-12-24
Abstract: 1. A process for minimising the number of squeezing and shut-in operations needed to inhibit scale and thereby increase the production rate from an oil well using the precipitation squeeze method, said process comprises injecting into an oil-bearing rock formation matrix a water-miscible formulation comprising: (a) a water-miscible surfactant which is in liquid form, (b) a solution of a water-soluble metal salt comprising a multivalent cation and  (c) a solution of a water-miscible scale-inhibiting compound comprising an anionic component capable upon injection into in the rock formation matrix in the presence of the cations of component (b) to form a scale inhibiting precipitate in situ, characterized in that the surfactant (a) is a glycol ether and the minimum ion concentration of the scale inhibiting compound (c) is 5000 ppm based on the total weight of the formulation, said components (a) - (c) being introduced either as a pre-formed single homogeneous composition, or simultaneously in parallel or sequentially in either order into the rock formation matrix. 2. A process according to claim 1 wherein the glycol ether is an alkyl glycol ether in which the alkyl group is straight or branched chain and has 3-6 carbon atoms. 3. A process according to any one of the preceding claims wherein the glycol ether comprises one or more ethers selected from the group: ethylene glycol mono ethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-2-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol monoisopropyl ether, di ethylene glycol mono-n-butyl ether, diethylene glycol mono-isobutyl ether, diethylene glycol mono-2-butyl ether, diethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-pentyl ether, diethylene glycol mono-2-methylbutyl ether, diethylene glycol mono-3-methylbutyl ether, diethylene glycol mono-2-pentyl ether, diethylene glycol mono-3-pentyl ether, diethylene glycol mono-tert-pentyl ether, triethylene glycol mono butyl ether (n-butyltriglycol ether), tetraethylene glycol mono butyl ether (n-butyltetraglycol ether) and pentaethylene glycol mono butyl ether (n-butylpentaglycol ether). 4. A process according to any one of the preceding claims wherein the water-soluble metal salt (b) comprising multivalent cation is a salt of a metal from Group II or Group VI of the Period Table. 5. A process according to any one of the preceding claims wherein the water-soluble metal salt (b) is a salt of one or more metals selected from copper, calcium, magnesium, zinc, aluminium, iron, titanium, zirconium and chromium. 6. A process according to any one of the preceding claims wherein the water-soluble metal salt (b) is selected from the halides, nitrates, formates and acetates of the metals. 7. A process according to any one of the preceding claims wherein the water-soluble metal salt (b) is calcium chloride, magnesium chloride or mixtures thereof. 8. A process according to any one of the preceding claims wherein the solution of the water-soluble metal salt (b) is an aqueous solution. 9. A process according to any one of the preceding claims wherein the water-miscible scale-inhibiting compound (c) comprising an anionic component capable of forming in the presence of the cations in (b) a scale inhibiting precipitate in situ upon injection into in the rock formation matrix is a water-soluble organic one, molecule of which has at least two (I) carboxylic acid groups and/or (II) phosphonic acid groups and/or (III) sulphonic acid groups. 10. A process according to claim 9 wherein compound (c) has from 2 to 30 carboxylic acid and/or phosphonic acid and/or sulphonic acid groups. 11. A process according to any one of the preceding claims wherein the scale inhibiting compound (c) is an oligomer, polymer or monomer with at least one hydroxyl group and/or amino nitrogen atom. 12. A process according to claim 11 wherein compound (c) is hydroxycarboxylic acid, a hydroxy- or amino-phosphonic acid or sulphonic acid. 13. A process according to claim 12 wherein compound (c) is selected as one or more compounds from the group, including: polyphosphino carboxylic acids, polyacrylic acids, polymaleic acids, other polycarboxylic acids or anhydrides, polyvinyl sulphonates and co- and ter-polymers thereof, phosphonates, polyaminoethylenephosphonic acids, 1-hydroxyethylidene-1,1-diphosphonic acid, organophosphate esters and phosphomethylated polyamines. 14. A process according to claim 12 wherein compound (c) is selected as one or more compounds from the group: lactic acid, citric acid, tartaric acid, maleic anhydride, itaconic acid, fumaric acid, mesaconic acid, citraconic acid, polyvinylsulphonate/polyacrylic acid copolymers, polyvinylsulphonate/polyacrylic acid/polymaleic acid terpolymers, polyvinylsulphonate/polyphosphinocarboxylic acid copolymers, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, nitrilotrimethylene phosphonic acid, diethylenetriaminepentamethylenephosphonic acid, N,N'-bis[3-aminobis(methylene phosphonic acid) propyl], ethylenediaminebismethylenephosphonic acid and phosphate esters of polyols, containing one or more 2-hydroxyethyl groups. 15. A process according to claim 12 wherein compound (c) is an aliphatic phosphonic acids having 2-50 carbon atoms.  16. A process according to claim 15 wherein compound (c) is a polyaminomethylenephosphonates having 2-10 N atoms, each of the nitrogen atoms optionally bearing at least one methylenephosphonic acid group. 17. A process according to any one of the preceding claims wherein the scale inhibiting compound (c) is at least partly in the form of its alkali metal salt. 18. A process according to any one of the preceding claims wherein the minimum ion concentration (hereafter "MIC") of the scale inhibiting compound (c) used is at least 10000 ppm based on the total weight of the formulation. 19. A process according to any one of the preceding claims wherein the pH value of the formulation is so controlled that prior to introduction thereof into the rock formation matrix the components of the formulation are in solution whereas upon injection into the rock formation matrix and under the conditions of pH and temperature, prevalent or created in said matrix, the pH of the solution varies to a value so as to generate in situ a precipitate of the scale inhibitor when compound (c) is in contact with the compound (b). 20. A process according to claim 19 wherein:  (a) the solution comprising compounds (b) and (c) in the formulation is highly acidic and (b) the aqueous system surrounding the rock formation matrix has a relatively less acidic or an alkaline pH value, insufficient to enable precipitation of the scale inhibitor in situ upon injection of the formulation into the rock formation matrix, whereby (c) njecting into the rock formulation matrix a solution of a further compound which is heat sensitive and is capable of decomposing under the thermal conditions in the rock formation matrix so as to generate a basic compound thereby influencing the prevalent pH value in the rock formation to facilitate the formation of precipitate of the scale inhibitor in situ. 21. A process according to claim 20 wherein heat sensitive compound is urea or derivatives thereof. 22. A process according to any one of the preceding claims wherein components (a), (b) and (c) are sequentially introduced into the rock formation matrix, such that a slug of glycol ether (a) is injected into the formation matrix first, followed by a slug of scale inhibitor forming components (b) & (c), optionally placing a spacer of seawater between the two slugs of the main treatment.  23. A formulation comprising in an aqueous medium  (d) at least one surfactant comprising n-butyltriglycol ether in an amount of 1-45% w/w of the total formulation (e) a solution of a water-soluble metal salt comprising a multivalent cation and (f) a solution of a water-miscible scale-inhibiting compound in an amount of 1-25% w/w of the total formulation and comprising an anionic component capable of forming the scale inhibiting precipitate in situ in the presence of the cations of(e) upon injection into in a rock formation matrix, characterised in that the minimum ion concentration of the scale inhibiting compound (f) in said formulation being at least 5000 ppm based on the total weight of the formulation. 24. A formulation according to claim 23 wherein the surfactant (d) is present in the formulation in an amount ranging from 1-45% by weight. 25. A formulation according to claim 23 wherein the surfactant (d) is a byproduct stream from a glycol ether manufacturing processes which stream contains a high proportion of an alkyl triglycol ether. 26. A formulation according to claim 23 wherein the alkyl triglycol ether is n-butyltriglycol ether and the by-product stream comprises about 75% w/w ofn- butyltriglycol ether, about 2.5% w/w of butyldiglycol ether, about 19% of butyl tetraglycol ether and about 2% of butyl pentaglycol ether. 27. A formulation according to any one of the preceding claims 23-26 wherein said formulation is a homogeneous solution optionally comprising small amounts of a solubilizina agent to maintain the homogeneity of the solution during storage and transportation thereof. 28. A formulation according to claim 27 wherein the solubilising agent is a lower aliphatic alcohol which is present in an amount sufficient to maintain the homogeneity of the formulation in solution. 29. A formulation according to claim 26 or 27 wherein the solubilising agent is methanol or ethanol. 30. A formulation according to any one o the preceding claims 23-29 wherein the aqueous medium in the formulation is derived from fresh, tap, river, sea, produced or formation water, with a total salinity ranging from 0-250g/1. 31. A formulation a